Magnesium oxide (magnesia) has been utilized as refractory materials, and also as various additives, electronic component applications, phosphor source materials, source materials for various target substances, source materials for superconducting thin film substrates, tunnel barrier source materials for tunnel magnetic resistive elements (TMR elements), protective film source materials for color plasma display panels (PDPs), as well as source materials of crystal magnesium oxide layers for PDPs, and has attracted attention as an inorganic material having a very wide variety of applications. In recent years, magnesium oxide powders having a large crystallite diameter, an extremely small crystal strain and a favorable crystallinity, which can sufficiently exhibit a variety of characteristics of magnesium oxide such as insulating properties, fluorescent properties, transparency and the like in various applications have been demanded.
Known methods for producing magnesium oxide powders predominantly include: (1) a gas phase method by oxidation of metal magnesium; (2) a thermal decomposition method by baking a precursor such as magnesium hydroxide or magnesium carbonate at a temperature no lower than a thermal decomposition temperature; and (3) a method in which an agglomerate obtained by an electromelting method is pulverized.
However, according to such conventional methods, although magnesium oxide powders composed of single crystals having some level of size could be obtained, their size is not necessarily satisfactory, and magnesium oxide powders also having a favorable crystallinity cannot be produced.
As magnesium oxide powders having a favorable crystallinity, Patent Document 1 discloses magnesium oxide powders having a peak width at half-height (half-power band width) of the peak on a (200) plane in powder X-ray diffraction carried out using a Cu—Kα ray falling within the range of 0.40 to 0.60 degrees, and Patent Document 2 discloses magnesium oxide powders having a peak width at half-height of the X-ray diffraction peak at a Bragg angle (2θ±0.2 deg) of 42.9 deg (on a (200) plane) determined with a powder X-ray diffraction method carried out using a Cu—Kα ray falling within the range of 0.25 to 0.52 deg. However, these magnesium oxide powders do not yet have a sufficient level of crystallinity.    Patent Document 1: JP-A No. 2003-229132    Patent Document 2: JP-A No. 2007-065245